INTERMAP is basic epidemiologic investigation designed to help clarify unanswered questions on the role of dietary factors, particularly macronutrients, in the etiology of unfavorable blood pressure (BP) levels prevailing for a majority of middle-aged and older individuals in the U.S. population. A particular focus -- within the context of this overall objective -- is to help elucidate the role of these dietary factors in accounting for the even more adverse BP patterns of less educated population state, e.g., in the U.S. both less educated African-Americans and Whites. INTERMAP aims to achieve a major advance on these important issues, based on its design, patterned after the tested INTERSALT model: large sample size of 5,200 persons (2,600 men and 2,600 women), ages 40-59 from 20 diverse population samples of varied ethnicity, SES, and dietary habits in 4 countries (China, Japan, U.K., U.S.) (260 persons per sample). Cost effectiveness is assured by major cost-sharing by non-U.S. centers, so that costs for NHLBI are much less than for research of this scope done solely in the U.S.
Specific aims i nvolve elucidating influences on BP of amount and type of protein, lipids, carbohydrates, also amino acids, Ca, Mg, antioxidants, fiber, caffeine. Primary hypotheses to be tested, with control for BMI, intake of alcohol, Na, K, age, sex, other confounders are; dietary protein is inversely related to BP; inverse relations between education and BP are significantly accounted for by education-correlated differences in dietary protein intake; there is a direct relation to BP of dietary SFA, cholesterol, keys score, starch; there is an inverse relation of PFA and of P.S. Participants, randomly selected, are to provide 2 timed 24-hr urine collections for assessment of Na, K, creatinine, urea, and are to complete four 24-hr dietary recalls. BP is to be measured twice at each of 4 clinic visits. The study is to be coordinated by two Coordinating Centers -- Northwestern University, Chicago and london School of Hygiene and Tropical Medicine. Urinary determinations are to be made at a Central Laboratory in Leuven, Belgium. 24-hr dietary recalls are to be converted into nutrients with use in each country of an up-to-date, extensive, high- quality, well-maintained national data base on nutrient composition of foods and recipes, with international study-wide standardization, quality control, and support for this and related local and national tasks. Data analyses o test hypotheses and explore nutrient-BP relations are to be done at the london Coordinating Center. Findings on relations of multiple dietary factors to BP are to be used to estimate favorable impact on BP of multiple improvements in nutrition by populations. This, in turn, should aid in making dietary recommendations toward achieving the goal of primary prevention of hypertension, and shifting BP distributions downward to avoid excess risk associated with present levels generally above optimal.
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